1. Field of the Invention
The present invention relates to a removing solution for removing metals containing copper, silver or palladium, a washing method for a semiconductor substrate using the removing solution, and a process for producing a semiconductor device.
2. Description of the Related Art
The requirement for high-speed operability of semiconductor device has increased year by year, and currently copper of low resistance is in wide use as a wiring material. Copper alone has low resistances to electromigration and stress migration and tends to cause disconnection when a fine wiring is employed. However, by adding, for example, tin (Sn), zirconium (Zr) or silver (Ag), resistances to electromigration and stress migration can be enhanced. As for silver which has a lower resistance than copper, its use as a main component of a wiring material is being investigated.
Copper and silver have a property of low resistance; however, they may incur metal contamination which results in reduced reliability of device, in a process for formation of semiconductor device. A countermeasure for such metal contamination is an important technical task.
When silver or copper is used as a wiring material, metal contaminants of silver, copper, their compounds, etc. adhere to the back side of substrate, etc. in a metal layer formation step and a processing step. In the subsequent heat treatment step, such metal contaminants diffuse through the substrate and reach its device area, deteriorating the properties of the device and causing current leakage. The diffusion of metal contaminants appear strikingly when the heat treatment is conducted at a high temperature of, for example, 300° C. or more. Further, when a semiconductor substrate is transferred in a carrier system that metal contaminants have adhered to the substrate, cross-contamination of film-forming apparatus takes place.
Thus, when a step of forming a metal layer containing silver or copper is included, it is desired to wash the back side, etc. of substrate to a highly clean state.
However, metal contaminants including silver, copper and compounds thereof adhere to a silicon substrate strongly in some cases and are generally difficult to remove. Further, in order to efficiently remove metal contaminants adhering to a silicon substrate, it is desired to not only dissolve the metal contaminants but also effectively prevent readhesion of the dissolved metal contaminants to the silicon substrate.
The present invention has been made in view of the above situation and aims at providing a removing solution which can dissolve and remove metal contaminants such as silver, copper and the like sufficiently and further can highly prevent readhesion of the dissolved metal contaminants, and a washing method for a semiconductor substrate.